Conventionally, photoconductive layers applied to electrographic photoreceptors frequently use the photoconductive materials of inorganic systems such as Se, CdS, ZnO and the like However in the case when these inorganic compounds are used as photoconductive layers of electrographic photoreceptors, they are not necessarily satisfactory from the point of view of heat resistance, durability, and toxicity. In recent years, extensive studies have been made for utilizing organic system photoconductive materials as a photosensitive layer on electrographic photoreceptors in place of the inorganic system photoconductive materials. Especially, when an organic system photoconductive material is used as a photosensitive layer of an electrographic photoreceptor, the electrographic photoreceptor becomes flexible, and easy to produce, and it allows a cheaper electrographic photoreceptor.
However, it is the present status of the art, that a photoreceptor which can satisfy the variety of characteristics required for an electrographic photoreceptor, such as sensitivity, durability or the like at a time, has not yet been found.
First, as the technology which can improve the durability of the electrography photoreceptor using the organic system photoconductive substances are known a number of technologies.
There is, for example, disclosed in the Japanese Patent Publication Laid-Open No. 157/84, a technology which improves the repetition characteristics by adding N, N-disubstituted dithiocarbamate in the photosensitive layer. This technology has a certain degree of effect on the O.sub.3 degradation, but has a conservancy disadvantage under high temperature and high humidity which lowers the sensitivity.
Further, in Japanese Patent Laid-Open No. 218447/84, there is disclosed a technology in which the repetition stability of electric potential is improved by adding amine to the composition of a photosensitive layer. However, this technology has the disadvantage of lowering sensitivity.
Further still, in Japanese Patent Publication Laid-Open No. 166351/83 and No. 166352/83, there are disclosed technologies in which a polymer of a specified quarternary ammonium salt is used as a binder resin for charge-generating substances. However, this technology requires to control reactivity, compositions or the like, so that it has the disadvantages of lacking production stability, having large fluctuation of characteristics and the lowering sensitivity.
Also, in recent years, laser beam printers which utilize the electrophotographic process and form images by using laser light as an optical source have been developed. Gas lasers of He-Ne, Ar, etc., or semiconductor lasers as the laser light source. As the photoreceptor for these laser beam printers, an electrographic photoreceptor for usual light source can be utilized, when the wavelength of the laser light source agrees to the spectral sensitivity range of the receptor.
But, since the laser light potentially causes interference, a new problem has occurred; that is, since the laser light interferes with the conductive base body on the surface of the photoreceptor, there is produced a pattern known as "moire" in the printed picture image, and the quality of the picture degrades significantly. The phenomenon of moire becomes an especially significant fault in the case when a semiconductor laser is used as a light source.
The moire pattern is the result of the interference of the repetitive reflection light at the air-photosensitive layer interface and the Al-layer surface, and it is considered that when the refelected light from the air-photosensitive layer interface and the reflected light from the Al interface have the same degree of strength, the interference fringes show maximum contrast, and in a half tone picture image, a so-called grain pattern is observed.